1. Field of the Invention
The present invention relates in general to vehicular headlamps, and more particularly to vehicular headlamps of a so-called "projector type" which comprises a light source for producing light, a concave reflector for reflecting the light forward, a shade plate located in front of the concave reflector for partially shading and thus contouring the reflected light, and a converging lens located in front of the shade plate for projecting the contoured light beam forward. More specifically, the present invention is concerned with the projector type vehicular headlamp which has two light sources, one being for the high beam and the other being for the low beam.
2. Description of the Prior Art
In order to clarify the task of the present invention, one conventional projector type headlamp "a" will be described with reference to FIGS. 12A, 12B, 13A and 13B of the accompanying drawings.
As is schematically illustrated in FIGS. 12A and 12B, the headlamp "A" comprises a concave reflector "b" including an upper reflector part "c" and a lower reflector part "d". Each part "c" or "d" has a light reflecting layer lined on an ellipsoidal inner surface thereof. That is, the inner surface of each reflector part "c" or "d" constitutes a part of the outer surface of an ellipsoid of revolution. The upper and lower reflector parts "c" and "d" have a common optical axis "X--X" and a common second focus "F.sub.2 ". The first focus "F.sub.1 " of the upper reflector part "c" is positioned in front of the first focus "F.sub.1 '" of the lower reflector part "d".
Designated by reference "e" is a filament of an electric lamp which produces light for a low beam. The filament "e" is positioned on the first focus "F.sub.1 " of the upper reflector part "c" and extends along the optical axis "X--X". Designated by reference "f" is a cover which conceals front and lower portions of the filament "e". Thus, light rays "g" produced by the filament "e" are directed only upward, that is, toward the upper reflector part "c" and reflected forward by the same and converged at the second focus "F.sub.2 ".
Designated by reference "h" is a filament of an electric lamp which produces light for a high beam. The filament "h" is positioned on the first focus "F.sub.1 '" of the lower reflector part "d" and extends along the optical axis "X--X". Thus, light rays "i" projected downward from the filament "h" are reflected forward by the lower reflector part "d" and converged at the second focus "F.sub.2 ", while, light rays "j" projected upward from the filament "h" are reflected forward by the upper reflector part "c" and thus directed forward passing along paths located above the second focus "F.sub.2 ".
Designated by reference "k" is a shade plate which is arranged perpendicular to the optical axis "X--X". The shade plate includes an upper edge "1" which is, as is seen from FIG. 2, positioned just behind the second focus "F.sub.2 " and in contact with the optical axis "X--X". Accordingly, light rays directed forward are partially intercepted or contoured by the shade plate "k".
Designated by reference "m" is a converging lens which is positioned in front of the shade plate "k". The lens "m" has its focus "F.sub.c " located at generally middle portion of the upper edge "1" of the shade plate "k". Thus, the light beam projected forward from the converging lens "m" has a cross-sectional pattern contoured by the shade plate "k". That is, the converging lens "m" makes an upside-down image of the shade plate "k" in the projected light beam.
When, thus, the filament "e" is energized, the headlamp "a" projects a light beam or low beam which has such a contoured cross-sectional pattern "n" as shown in FIG. 13A. It is to be noted that the upper edge "o" of the pattern "n" is produced by the provision of the upper edge "1" of the shade plate "k".
While, when the other filament "h" is energized, the headlamp "a" projects a light beam or high beam which has such a contoured cross-sectional pattern "p" as shown in FIG. 13B. That is, the pattern "p" comprises an upper portion "q" produced by the light rays "i" from the lower reflector part "d" and a lower portion "r" produced by the light rays "j" from the upper reflector part "c".
However, due to its inherent construction, the headlamp "a" has the following drawbacks.
That is, the high beam produced by the headlamp "a" fails to have a satisfied quantity of light.
Since, in the headlamp "a", the shade plate "k" is arranged perpendicular to the optical axis "X--X" of the light reflector "b", the light rays "i" produced by the filament "h" and reflected forward by the lower reflector part "d" are considerably intercepted by the shade pate "k" during travelling toward the converging lens "m". Intercepting the light rays "i" brings about a wasteful usage of the light rays produced by the light source.
Furthermore, as is understood from FIG. 13B, since the light rays "i" reflected by the lower reflector part "d" and the light rays "j" reflected by the upper reflector part "c" are all used for producing the contoured cross-sectional patterns "q" and "r" which are directed toward a portion below the horizontal line "H--H", the light beam from the headlamp "a" shows a poor illumination ability in illuminating objects positioned above the horizontal line "H--H".